Three major aspects of immune complex biology have been studied. First, the ability of the mouse liver to handle infused complexes was studied, using site-specifically cross-linked model complexes. The receptors for complexes on Kupffer cells were found to be specific for the immunoglobulin molecule and not other aggregated proteins removed by the same cells. Furthermore, NZB/W mice, with murine lupus, show an impaired ability to injest complexes after they are bound to Kupffer cells. Second, the influence of antigen or the handling of complexes has been studied using pairs of glycoprotein antigens differing only in their carbohydrate side chains but reacting with the same antibodies to form complexes. Desialylated glycoproteins carry complexes to hepatocytes, whereas complexes with the intact protein go to Kupffer cells. Third, the influence of monosaccharides substituted onto the Ficoll backbone of another group site-specifically cross-linking antigens has been studied. Galactose substitution on the antigen carries the stable complexes to hepatocytes, whereas mannose brings them to Kupffer cells.